1. Field of the Invention
The present invention relates to a display controlling apparatus, and particularly to a display controlling apparatus suitable for controlling a display having a memory function for displaying an image at a lower frequency than the frame frequency of an input image signal, for example, a ferroelectric liquid crystal display (hereinafter abbreviated to as FLCD).
2. Related Background Art
First, FLCD will be described briefly. FLCD is a display using a liquid crystal, characterized in that each pixel itself of the display has a memory, whereby each pixel cell can hold its display state without application of electric field, with the display state of each pixel being changed by applying an electric field. FLCD is expected as a display in the next generation because it is easily manufactured into a large screen.
Recently, several binarization methods have been developed, including an error diffusion method and an average density preservation method, whereby a high quality binary image can be obtained even though the image may contain characters, line figures and natural images mixed with each other.
FLCD can not operate at the display speeds of high definition, for example, 60 Hz non-interlace for the image size of 1280.times.1024, due to its characteristics. In particular, for computer display outputs from the work station which has recently advanced for higher definition, FLCD can not follow the cursor movement of a mouse requiring the interactiveness, with a frame frequency of about 1/4, so that the operator may feel unpleasant because the operation efficiency is decreased.
Thus, a method has been devised, with improved apparent frequency, in which the display state is altered for only the changed portion between frames by making effective use of the memory function of the FLCD.
FIG. 2 shows the relation between a computer and a display. 10 is a computer main unit, comprised of a CPU and peripheral units such as a memory and a disk. From the computer main unit, an image signal 11 for display is output. Normally, the image signal 11 is a digital signal, or an analog signal, such as an NTSC composite signal, a component RGB signal and a non-interlace signal. 30 is an FLCD. 20 is an image process unit, according to the present invention, for inputting an RGB analog signal 11 from the computer main unit 10 for the conversion into digital signal 12, one bit for each RGB, which is then output to the FLCD 30. The FLCD 30 inputs the digital RGB signal 12 for the display from the image process unit 20.
However, in the configuration as shown in FIG. 2, the output from the computer 10 is an analog signal of 60 Hz non-interlace with the image signal 11 corresponding to the size of 1280.times.1024, for example, wherein information regarding the shape of cursor or the movement from (X0, Y0) to (X1, Y1) is not specifically given, even though the cursor is moved as shown in FIG. 6. That is, no information regarding the area to change the display state to effect the fast display is supplied from the computer.
Hence, such information must be extracted out of the input image data.
In particular, when the image data is displayed through quantization, it is a problem how to extract the area to change the display state.
On the other hand, a technique for switching between the intraframe coding and the interframe coding depending on whether or not the display state is changed has been described in a newly filed application based on Japanese Patent Application Nos. 4-149470 and 4-292214.
However, the above-cited technique needed no information as to which area of the screen was changed. Therefore, it could not detect such changed area which is of concern in the present invention.